AR-30 Differences Between Calibers?

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I'm still on the fence about buying a AR-30 in 300WM versus 338 Lapua. I really want the 338, but I found a heck of a deal on a 300 WM. What I want to know is, can an AR-30 in 300WM be converted to 338 with just a barrel and bolt head change ? Are the mags and mag openings the same size ? What about the receivers ? I hope someone can help. Thanks.